Generally, polycarbonate and vinyl copolymer resin blend compositions can provide improved processability while maintaining high notched impact strength. Such resin blend compositions should also have good flame retardancy as well as high mechanical strength when used in the production of heat-emitting large-size injection molded products such as computer housings, office supplies, and the like.
A halogen-containing flame retardant and an antimony-containing compound can be added to the resin compositions to impart good flame retardancy. However, halogen-containing flame retardants can produce toxic gases during combustion. Therefore, there is an increased demand for the resin without a halogen flame retardant due to the harmful health effects of the gas.
A well known and widely used method of imparting flame retardancy without using halogen-containing flame retardants uses a phosphate ester flame retardant. U.S. Pat. No. 4,692,488 discloses a thermoplastic resin composition comprising a halogen-free aromatic polycarbonate resin, a halogen-free styrene-acrylonitrile copolymer, a halogen-free phosphorous compound, a tetrafluoroethylene polymer and a small amount of ABS copolymer. U.S. Pat. No. 5,061,745 also discloses a flame retardant resin composition comprising an aromatic polycarbonate resin, an ABS graft copolymer, a styrene copolymer, phosphate ester and a tetrafluoroethylene polymer. However, the resin compositions described above have a disadvantage in that it is necessary to add an excessive amount of phosphoric ester flame retardant in order to obtain an acceptable level of flame retardancy.